Researched On Fatigue Life Of Metals Based On The Combined Theory Of Strength And Stability

This paper is concerned at research on the Combined Theory of Strength and Stability (CTSS).The key point of research is connotation of CTSS and its application in similarity of mechanics performance, fatigue life, fracture mechanics and dealing with the experimental datum. The major work is as follows:(1) By inducing four phrases, the content and calculate method of CTSS are simplified. Besides these, the whole system of CTSS and its methodology are displayed clearly. Using the parameterΦ1 named tangent modulus factor to calculate the ultimate strength of the pressure hull of deep-sea submersible, the problem such as material nonlinearity of titanium alloy, geometrical nonlinearity and moderately thick shell can be solved easily. At last, the calculated values are compared with Finite Element Method results and experimental data.(2) Analyzing a great deal of material performance curves of ship structural metals and aircraft structural metals, the equilibrium state parameters curves of non-dimensional stress and fatigue life are established. Through the parametric expression of material performance curve, similar law among different material is found. It can be expressed and to calculate local strain by PL(c, m) model.(3) By applying derived Proportional Law and S-N curves, the parametric expression of fatigue is established. Based on the corresponding relationship of equilibrium state parameterΦt and fracture toughness KIC, the equivalent crack length about stress fatigue life and strain fatigue life is obtained.(4) Comparing and researching the modeling method between CTSS and gray theory, the modeling method of CTSS can be also used to analysis and predict the fatigue life of different material. More, it can be used to gray correlation analysis at feature point of fatigue life nearby yield stress.(5) Introducing the nonlinear method of CTSS to facture mechanics, a calculate method to solve elastic-plastic fracture is established based on the parameter comparison and analysis between CTSS and fracture mechanics. Compared with classical solution such as COD method, J integral and so on, all kinds of COD design curves,Φt～εexpression of formula and Kcr～Φt(φ) curve for safety assessment are established.(6) Based on stress-strain relationship and used PL(c, m) model, the correlative experimental datum, regular expressions and experiential formula of pressured structures such as compression bar, compression plate, stiffened plate, cylindrical shell, can be sorted and explained by new methods. Based on the similar law, the experimental datum on fatigue life of nonsymmetry cycle are described and researched by using CTSS. Besides, the datum of fracture mechanics can be dealt with by using this theory and its solution which is verified by some experiential formula.